Heat transfer fluids are used in a variety of applications including reactor cooling/heating, plastic molding, constant temperature baths, automotive coolant systems, cold storage, climactic chambers, heating, air-conditioning, etc. The primary objective of a heat transfer fluid is to remove heat from the source and transfer the heat to a sink. In a typical heat transfer fluid loop, the heat transfer fluid is pumped through heat exchangers or jackets. The heat transfer fluid either adds or removes heat from the process thereby maintaining a stable temperature.
Non-aqueous heat transfer fluids are normally used in extremely low or high temperature applications where water-based heat transfer fluids cannot operate due to freezing or boiling problems. Non-aqueous heat transfer fluids have lower heat transfer efficiency compared to water-based fluids because the non-aqueous heat transfer fluids have lower specific heat and thermal conductivity compared to the water-based heat transfer fluids. Improving the efficiency of a heat transfer process by 20% to 25% could lead to significant savings in energy and equipment. Hence, there is a need for improving the efficiency of the heat transfer fluids.
Nano-additive particles made from copper, silver, and iron suspended in a heat transfer fluid improve the thermal conductivity as well as convective heat transfer coefficient of that fluid. However, the nano-additive particles do not disperse well in the heat transfer fluid due to their significant density difference with the carrier fluid. When surfactants are used to disperse nano-additive particles in the heat transfer fluid, the surface of the nano-additive particles gets covered with the surfactant and diminishes the effectiveness of the nano-additive particles for enhancing the thermal conductivity of the heat transfer fluid.
Another common problem associated with non-aqueous heat transfer fluids is the presence of moisture in the heat transfer fluid. Moisture could enter into the heat transfer fluid during installation, or when the heat transfer fluid is re-circulated during the operation of the system. When a heat transfer fluid goes through temperature cycles, the expansion and contraction of the heat transfer fluid allows outside air to contact the heat transfer fluid. This inflow of outside air into the re-circulating heat transfer fluid adds moisture to the heat transfer fluid. In low temperature applications, the moisture can freeze and form ice crystals in the heat transfer fluid and cause problems in the re-circulating heat transfer fluid loop. Moisture can also result in degradation of the heat transfer fluid. In certain applications, such as in dielectric switches, a very low concentration of moisture is desired in the heat transfer fluid in order to maintain a very high dielectric strength of the heat transfer fluid. Therefore, removal of moisture from heat transfer fluids, or maintenance of moisture at a certain reduced level is a concern. Existing methods remove moisture from a non-aqueous heat transfer fluid by passing the heat transfer fluid through a bed of the desiccant or molecular sieve. This method could be used in-line or as a bypass stream of the primary heat transfer fluid loop. If a desiccant bed is used in-line, the pressure drop in the re-circulating heat transfer fluid loop increases, thus requiring the use of a higher horsepower pump. Additionally, the system/process must be shut down completely in order to change the desiccant from the re-circulating system. If the desiccant bed is used in a by-pass stream, that is, a slip-stream, the flow rate of the heat transfer fluid in this stream is much smaller than the flow rate in the main heat transfer fluid loop, which in turn requires an extended time, sometimes months, for removal of the moisture present in a non-aqueous heat transfer fluid.
Hence, there is long felt but unresolved need for a heat transfer fluid that provides better heat transfer efficiency than its base or carrier fluid and that maintains the moisture content of the carrier fluid below a threshold level.